I thought women were supposed to be the fairer sex, so what does this woman have ice in her veins?

I was reading a tabloid paper at work, and the paper was reporting on the fiasco that is the Giggs brothers scandal and was delving into all the horrendous details. This woman was shagging her brother in law for 8 years, slept with 3 other footballers, and had a week long affair whilst on a clubbing holiday. Her husband was in love with her, and by all accounts she's a "nice girl". How could she be so heartless? That's the worst thing about women like this, they seem so nice, they look pretty, are fun to be around, act like butter wouldn't melt in their mouth, and then BANG, they shag your brother for 8 years. Please confirm for me that this is rare, because I know lots of "nice girls".